Frogeye leaf spot

Cercospora sojina

Cercospora sojina is a fungal pathogen that causes frogeye leaf spot, a common and economically significant disease in soybean (Glycine max) crops. Here's an informative description of Cercospora sojina, including its appearance, identification, and management:

1. Symptoms:

  • Leaf Lesions: Frogeye leaf spot symptoms typically begin as small, round, dark lesions with a reddish-brown to purplish margin.
  • Lesion Expansion: Lesions can expand, becoming larger and developing a gray to tan center with a darker border, resembling a "frogeye" appearance.
  • Leaf Yellowing: Surrounding the lesions, yellowing of the leaf tissue may occur, contributing to the characteristic appearance.

2. Disease Cycle:

  • Overwintering: The fungus can overwinter on infected crop debris.
  • Infection: In the spring, spores (conidia) produced on infected residues or other infected plants initiate new infections.
  • Spread: The disease can spread through rain splashes, wind, and agricultural practices.
  • Secondary Infections: Secondary infections may occur during the growing season, and the fungus may produce more spores.

3. Identification:

  • Distinctive Lesions: Identification often begins with the observation of distinctive round lesions with a gray to tan center and a darker border.
  • Frogeye Appearance: The characteristic "frogeye" appearance, with concentric rings of color, is a key identifier.
  • Leaf Yellowing: Yellowing around lesions further aids in identification.

4. Management:

  • Resistant Varieties: Planting soybean varieties that are resistant or less susceptible to frogeye leaf spot is a key management strategy.
  • Fungicide Applications: Fungicides can be applied preventively or curatively to manage the disease. Application timing is crucial, and a rotation of different fungicide classes helps reduce the risk of resistance development.
  • Crop Rotation: Avoiding consecutive cultivation of soybeans in the same field can help reduce the pathogen's survival.
  • Residue Management: Proper management of crop residues, including plowing under infected residues, can reduce the inoculum.

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